The production of cast resins, for example for the electrical industry, by reaction of organic polyisocyanates with polyhydroxyl compounds is already known (see, for example, Kunststoff-Handbuch, Vol. VII, "Polyurethane" by Becker/Braun Carl Hanser Verlag Munich, Vienna (1983) pages 410 to 425). Shaped articles of this type which are used, for example, as insulators in the electrical industry, must be substantially bubble-free and foam-free. According to the prior art, importance is placed on careful degassing and drying of the starting materials, in particular the polyhydroxyl compounds. Generally speaking, further water absorption agents such as (anhydrous) zeolites are also added to the reaction mixtures, in order to reliably prevent bubble formation caused by the reaction between isocyanate groups and water which takes place with elimination of carbon dioxide. Furthermore, the presence of water during hardening cannot be avoided in specific applications, for example in the case of cable casting compositions which have to be processed in the open air even during bad weather conditions. In this case, the conventional PUR casting compositions based on polyether polyols lead to marked foaming even if the starting materials are free from water, due to the use of water absorption agents, resulting in that the insulating effect of the cast resin is greatly impaired.
Foaming does not occur if castor oil is used instead of polyether polyols. However, this natural product is subject to great variations in quality and, furthermore, PUR molding compositions based on this polyester polyol are very susceptible to hydrolysis. A further disadvantage of the composition based on castor oil resides in the fact that they become brittle during prolonged storage at elevated temperatures (&gt;50.degree. C.). The poor behavior during thermal aging is due to the double bond contained in the ricinoleic acid. As a result, the cast resin compositions in the course of time, develop cracks which have a detrimental effect on the electrical insulating capacity.
As has now surprisingly been found, sulphonic acid ester group-containing polyhydroxyl compounds of the invention represent a novel type of organic polyhydroxyl compound having the above-mentioned advantages of castor oil without its disadvantages. According to the invention these polyhydroxyl compounds are obtained by a reaction of paraffin sulphochlorides with a polyhydric alcohol. When using these new polyhydroxyl compounds as the polyol component in cast resin formulations based on organic polyhydroxyl compounds and organic polyisocyanates, optionally along with conventional polyether polyols, bubble free products which also exhibit excellent stability to hydrolysis, are obtained on hardening of the cast resin composition even in the presence of water.
It is known that sulphonic acid esters can be produced by the reaction of sulphochlorides of aliphatic or aromatic sulphonic acids with aliphatic alcohols in the presence of hydrogen chloride acceptors (Organikum, 13th edition, page 608, VEB Deutscher Verlag der Wissenschaften). Sulphonic acid ester group-containing polyhyroxyl compounds based on paraffin-sulphochlorides and polyhydric alcohols have not yet been disclosed hitherto, however. Consequently, the excellent suitability of these polyhydroxyl cmpounds in cast resin formulations of the above-mentioned type was also completely unforeseeable.